Dinosaurs Evolve—and Fly 267were no transitional forms between them and other dinosaurs. He even made the same claim
in his 1995 book (1995:124).
Apparently Gish never bothers to read even the children’s books closely. Nearly every
book about dinosaurs illustrates a group of Triassic creatures called prosauropods, whose
very name (translated as “before the sauropods”) implies that they are primitive relatives
of the larger sauropods (fig. 12.2A). The best known of these is Plateosaurus from the Trias-
sic of Germany (fig. 12.2B), but there are another dozen genera found in Triassic beds all
over the world. Most of these creatures were only about 5–8 meters (15–25 feet) long, one-
fourth the size of the giant Jurassic sauropods, but larger than their ancestors. They have
the beginnings of a long neck and long tail but not yet the incredible neck or tail of the giant
sauropods. The limbs are classic sauropod in the construction of their fingers and toes, yet
they are not as robust, and the forelimbs are long and delicate enough that they apparently
could alternate between quadrupedal walking and rearing up on their hind legs in a bipedal
stance to use their hands. Only when the sauropods reached huge sizes were they forced to
walk entirely on all fours, and their limbs also become much more massive in support of
their huge body weight.
Even more primitive than Plateosaurus was Anchisaurus from the Triassic of Connecticut,
Arizona, and South Africa. It was only 2.5 meters (8 feet) long, just slightly larger than a
human, and had a still shorter neck and tail and even more delicate limbs and feet. In fact,
it is the perfect transitional form between the more lizard-like early saurischian dinosaurs,
such as Lagosuchus (which were much smaller, as we shall soon see). Yet despite its outward
appearance, its skull bears all the distinctive hallmarks of sauropods, and it already shows
many of the specializations in the vertebrae and especially in the hands and feet that will
later come to mark the sauropods. The early saurischians (the “lizard-hipped” dinosaurs)
were primarily bipedal, but Anchisaurus seems to have been capable of both stances, and Pla-
teosaurus was even heavier and more likely to be quadrupedal. We have not only a smooth
increase in size from the earliest known dinosaur Eoraptor (fig. 12.3B-D) to Anchisaurus to
Plateosaurus to the larger sauropods but also a smooth transition in the anatomical features
and in the stance from bipedal to quadrupedal as well.
The other main branch of the saurischians was the theropods, or the predatory dino-
saurs. These are all familiar to us from the giants like Tyrannosaurus rex and the Jurassic
predator Allosaurus, but there are dozens of different genera and species of all shapes and
sizes. Among the more aberrant were the “ostrich dinosaurs,” which had long legs, long
necks, and toothless beaked heads much the living ostrich, but they also had a long bony tail
(which no living bird has). Gish (1995:124) briefly mentions some of the primitive theropods
but clearly has not kept up with the times.
Despite Gish’s denials, some of the primitive theropods are actually excellent transi-
tional forms (fig. 12.3). They ranged from only 70 centimeters (2 feet) long (Compsognathus)
up to 3 meters (10 feet) long (Coelophysis), so most were about the size of a chicken up to the
size of an adult human (fig. 12.4). Unlike their big theropod descendants, they were lightly
built, with small heads, long necks, and slender gracile limbs and tails. Yet their skulls and
especially their hands (with their unique combination of only three fingers: the thumb, index,
and middle finger) and feet had all the anatomical specializations seen in later theropods.
From primitive theropods like Coelophysis, we can trace the theropod lineage even far-
ther back to Eoraptor (fig. 12.3B–D), Staurikosaurus, and Herrerasaurus (figure 12.3E), which are
built much like Coelophysis but do not yet have all the distinctive specializations of theropods.